1. Field of the Invention
The present invention relates to a vane pump. In particular, the present invention relates to a vane pump suitably used in an evaporation leak check system and the like.
2. Description of Related Art
Conventionally, there is known a vane pump that drives and rotates a rotor having vanes by using a motor to pressurize and discharge a fluid. For example, Patent document 1 (JP-A-2009-138602) describes a vane pump used for depressurizing or pressurizing an inside of a fuel tank in an evaporation leak check system that checks leakage of fuel vapor from the fuel tank. In such the system, pump performance of the vane pump easily affects system performance.
The vane pump has a rotor substantially in the shape of a circular cylinder accommodated in a pump chamber defined by an upper casing and a lower casing. A suction passage and a discharge passage are formed between the upper casing and the lower casing to provide communication between an inside and an outside of the pump chamber. A shaft of the motor is loosely fitted in a central hole of the rotor.
In the vane pump having the above-described construction, the rotor rotates in the pump chamber with rotation of the shaft. If the rotor rotates, the fluid outside the pump chamber is suctioned into the pump chamber through the suction passage. The suctioned fluid is compressed by the rotation of the rotor and discharged to the outside of the pump chamber through the discharge passage. At that time, negative pressure arises near the suction passage inside the pump chamber. If the negative pressure arises near the suction passage of the pump chamber, there is a case where the rotor inclines to the suction passage side and an orientation of the rotor during the rotation of the rotor changes. If the rotor inclines, a contact state between the vanes attached to the rotor and an inner peripheral wall of the upper casing changes. As a result, there is a possibility that air-tightness of spaces of the pump chamber partitioned by the vanes changes and pump performance changes. If such the vane pump is used for the evaporation leak check system, it becomes difficult to correctly check the leak of the fuel vapor.